Previously, spring.config.name was handled in such a way that its
value would replace the defaults. By constrast, spring.config.location
would add to the defaults.

Update the handling of spring.config.location so that it replaces the
defaults. This aligns its behaviour with spring.config.name. To allow
users to add additional locations a new property,
spring.config.additional-location, has been introduced. It behaves as
spring.config.location did prior to this change.

Closes gh-10595